Washington: Islamabad was adamant on its demand for an apology for a NATO air strike at a border post in which 24 Pakistani soldiers were martyred, Pakistani ambassador to the US Sherry Rehman has said.

The air strike on the Salala border post in November led Pakistan to close the NATO supply lines to Afghanistan through Pakistani territory and ask the US to vacate the Shamsi air base in Balochistan.

Talks are on for the restoration of the supply routes, Rehman said on the sidelines of a NATO summit in Chicago.

The NATO convoys were paying an average of about USD 250 per truck before the November incident that caused strains in the US-Pakistan relationship.

Pakistan is now demanding USD 5,000 for each truck, but US Defence Secretary leon Panetta has ruled out paying the amount.